Dawn probe spots unusual features on giant asteroid

Kate Taylor, 22nd March 2012

Scientists studying images of the giant asteroid Vesta are working to explain the existence of a number of bright spots.

Observations using NASA's Dawn spacecraft show unusual geologic features, some of which have never before been seen on asteroids. And while Vesta's one of the brightest objects in the solar system, some areas now appear to be nearly twice as bright as others, revealing clues about the asteroid's history.

"Our analysis finds this bright material originates from Vesta and has undergone little change since the formation of Vesta over four billion years ago," says Jian-Yang Li of the University of Maryland.

"We're eager to learn more about what minerals make up this material and how the present Vesta surface came to be."

The bright areas appear all over Vesta, but are concentrated in and around craters, varying from several hundred feet to around 10 miles across.

The team believes that rocks crashing into the surface of Vesta may have exposed and spread the bright material.

The observations also show a greater-than-expected variety of distinct dark deposits across Vesta's surface - dark gray, brown and red. They appear sometimes as small, well-defined deposits around impact craters, sometimes as larger regional deposits.

"One of the surprises was the dark material is not randomly distributed," says David Williams of Arizona State University.

"This suggests underlying geology determines where it occurs."

The scientists' best guess is that the dark materials seem to be related to impacts and their aftermath, with carbon-rich asteroids hitting Vesta at low enough speeds to produce some of the smaller deposits without blasting away the surface.

Higher-speed asteroids also could have hit the surface and melted the volcanic basaltic crust, darkening existing surface material. These dark materials suggest that Vesta may preserve ancient materials from the asteroid belt and beyond, possibly from the birth of the solar system.

"Some of these past collisions were so intense they melted the surface," says Brett Denevi of Johns Hopkins University.
"Dawn's ability to image the melt marks a unique find. Melting events like these were suspected, but never before seen on an asteroid."